Fig. 716.--Rough and grooved commutator due to improper brush adjustment and failure to keep brushes in proper condition.
Ques. How is an untrue commutator detected?
Ans. If the commutator be untrue, the fact will be indicated when the machine is slowed down by a visible eccentricity, or by holding the hand, or a stick in the case of a high tension machine, against the surface while revolving, when any irregularity or eccentricity will be apparent by the vibration or movement of the stick. The only remedy for an untrue commutator is to re-turn it in the lathe.
Ques. What should be done in case of high segments?
Ans. They should be gently tapped down with a mallet, and if possible the clamping cones at the commutator end should be tightened.
If it be impossible to hammer the segments down, they should be filed down to the same diameter as the rest of the commutator, or the commutator re-turned. For low segments, the only remedy is to pull out the segments, or turn commutator down to their level.
Ques. Explain the term "flats on the commutator."
Ans. This is the name given to a peculiar fault which develops on one or more segments of the commutator. It is not confined to dynamos of bad design or construction, but frequently appears on those of the highest class, and may be recognized as a "pitting" or "flattening" of one or more segments.
Ques. What is the effect of flats on the commutator?